Ecology: The study of how organisms interact with the environment and each other. We often look at different aspects of ecology such as:- population ecology - population growth, dynamics, predation.- community ecology - how do organisms interact with each other (competition & more)- ecosystems - what impact do organisms have on the environment or vice versa. How does energy move through a system, food webs, etc.- conservation biology - how can we best preserve organisms and their environment. Population ecology: First, a population. This can have variable definitions, but in ecology usually it’s a number of individuals in the same place:- deer population in Northern Virginia- mouse population on George Mason- etc.- but we can often mean larger groupings - human population, for example. Population density.- One of the first things we want to know is how many individuals are in the area we’re looking at.- defined as # of individuals / unit area - e.g., 100 people / square kilometer.- often we need to estimate this using sampling techniques such as mark-recapture:- catch as many individuals as possible. Mark them.- do it again, in the same area. If most individuals caught the second time are unmarked, this indicates a larger population than if they’re mostly marked.- we don’t need to know the equations for this.- Density often changes continually due to [Fig., not in text] :

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- birth, death, immigration, emigration (obviously true for human populations as well). Dispersal patterns [Fig. 36.2, p. 726] .- How are the organisms distributed?- clumped - occur in clumps, with few organisms between the clumps.- uniform - occur in a constant density (no matter where you look, there are about the same number.- random - they’re wherever they want to be (no pattern). Population growth.- We use mathematical models to describe how fast a population can grow. - Suppose we come up with the following hypothesis:- a single bacterium multiplies. Now we have two.- 20 minutes later each of those divides, and so we have four.- 40 minutes later, each of these four divides, so we have eight:- basically what we have is 2^x, where x is the number of times they divide (“^” means “exponent, so 2^x means 2 raised to the x power).- so at the end of 36 hours, we would have:

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